1. Field of the Invention
The invention relates to an improved apparatus for melting and dispensing hot melt type adhesives and sealants.
2. Description of the Prior Art
Apparatus for melting and dispensing hot melt type adhesives and sealants generally comprise a heated platen which fits inside the drum or container of hot melt material to be dispensed. The heated platen is pressed against the surface of the material contained in the drum, resulting in melting of the material. The melted material is forced through an orifice in the heated platen, pumped and dispensed where needed. Melters of the type described above are generally known. For example, models 5510 and 5520 from Nordson Corp. and models DP200 and DG200 from Meltex, Inc. are melters of this type.
One problem with the apparatus described above is that the heated platen includes an `O` ring seal which is sized to closely contact the inside wall of the drum and prevent leakage of molten adhesive as the platen is pressed downwardly into the adhesive. To insure a close fit and to prevent damage to the expensive `O` ring seal, care must be taken to position the drum properly. In order to do so, it has been found to be necessary to leave from about four to about eight inches of headspace in the drum. Otherwise, it would be difficult to position the fully loaded drum exactly central to the platen which does not have the same diameter as that of the drum. In addition, if a full drum were supplied without the headspace, as the heated platen would melt its way into the adhesive, the molten adhesive would fill the annular cavity between the outside of the platen and the inside of the drum. This molten material would be forced up and over the lip of the barrel until the `O` ring seal came into contact with the rim of the container and sealed it up.
With such apparatus, a drum cannot be completely filled because the headspace of about four to about eight inches must be left to accommodate the heated platen. The practice of only partially filling drums is wasteful, causing more drums to be filled and shipped as well as more frequent drum changes during operation of the melter dispenser.
With the advent of moisture curable compounds, the practice of partially filling drums presents even greater problems. Drums are normally filled by freshly processed materials which typically are warm or hot. As these materials cool they contract causing a vacuum which pulls in outside air. Because this outside air contains moisture, it can start the curing reaction which will result in surface skinning. Depending on the material, such skins can be very difficult to remove as well as being a waste of material.
It is an object of the present invention to provide an improved melting and dispensing apparatus which can accommodate completely filled drums.